In proteomics, a very important technique is to easily separate and handle a recombinant protein.
Nickel nitrilotriacetic acid (Ni-NTA) beads most frequently used to separate a recombinant protein have been most widely used to purify a protein with an oligohistidine affinity tag (His-tag). A NTA-attached resin is used to fix Ni ions in the Ni-NTA beads and separate a His-tagged protein through coordination chemistry.
In recent years, Xu et al. have synthesized an NTA-attached FePt nanoparticles and an NTA-attached Co/Fe2O3 magnetic nanoparticles and demonstrated the separation of a His-tagged protein by using the magnetic nanoparticles (C. Xu, K. Xu, H. Gu, X. Zhong, Z. Guo, R. Zheng, X. Zhang, B. Xu, J. Am. Chem. Soc. 2004, 126, 3392; C. Xu, K. Xu, H. Gu, R. Zheng, H. Liu, X. Zhang, Z. Guo, B. Xu, J. Am. Chem. Soc. 2004, 126, 9938).
Mirkin et al. have manufactured an Au—Ni—Au triblock nanorod using an anodic alumina membrane and applied it to magnetic separation of a His-tagged protein (K.-B. Lee, S. Park, C. A. Mirkin, Angew. Chem. 2004, 116, 3110; Angew. Chem. Int. Ed. 2004, 43, 3048; B.-K. Oh, S. Park, J. E. Millstone, S. W. Lee, K.-B. Lee, C. A. Mirkin, J. Am. Chem. Soc. 2006, 128, 11825).
However, in the methods published by Xu et al. and Mirkin et al., the nanoparticles for separating a protein are prepared through a series of complicated organic reaction processes.
In more recent years, Hyeon et al. have disclosed Ni/NiO core/shell nanoparticles for selectively binding and magnetically separating a His-tagged protein (I. S. Lee, N. Lee, J. Park, B. H. Kim, Y.-W. Yi, T. Kim, T. K. Kim, I. H. Lee, S. R. Paik, T. Hyeon, J. Am. Chem. Soc. 2006, 128, 10658).
However, the conventional systems have a problem in that the Ni/NiO nanoparticles should undergo a complicated multi-step organic synthesis process since Ni ions binding to a protein are introduced into surfaces of magnetic particles and a shell is formed around a core showing magnetism using silica or a polymer resin to connect a ligand. Also, when the Ni/NiO nanoparticles are recycled several times, the magnetic Ni core is gradually oxidized into NiO which is a semi-ferromagnetic substance. As a result, it is difficult to recycle the Ni/NiO nanoparticles as the magnetism of the Ni/NiO core/shell nanoparticles gradually decreases.
Meanwhile, a conventional method for preparing a ferrite powder includes mixing a metal oxide and drying, calcining and grinding the resulting mixture to prepare particles. However, the process should be performed at a calcination temperature of 1,200° C. or higher since an oxide is used as a starting material, and requires a long grinding process since compositions and particle size of the particles are not uniformly formed due to a solid-state reaction between the particles, which leads to degraded purity and magnetic characteristics caused by contamination.
In addition to the above-described method, methods for preparing a ferrite, such as coprecipitation, hydrothermal synthesis and a flux method, have been used. However, all the methods have problems in that it is difficult to mass-produce nanoparticles since an apparatus has a complicated configuration and is a batch-type apparatus, a manufacturing time is long, the nanoparticles do not exist as a composite since a new phase is formed by a reaction between raw materials, especially upon manufacture of nanocomposite powder, and it is difficult to obtain a powder having a uniform composition.